Band-pass filter for change of wave



Filed March 25, 19:57

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INVENTOR RUDOLF WEBER 7 ATTORNEY I Patented Sept. 1938 Rudolf Weber, Berlin, Germany, assignor Telefunken Gesellschait fiir- Drahtlose Telegraphic m. 11.11., Berlin, Germany, a corporation oi Germany Application March 25, 1931, Serial No. 132,901 In Germany March 12, 1936 3 Claims. (01. 178-44) The practical demand arises occasionally to S3 are closed, while switch Si is opened. The

make the band width of receivers changeable inside wide limits say, between 1 and k. c. This demand will be made, for instance, if in airplane 5 receiver apparatus a change is made from beam direction finding to the so-called impulse type of direction finding. In this'latter instance, the

impulses, in rectangular shape, must be faithfully reproduced in the Braun tube so that a wide-band must be received.

When a change to such a wide band is made,

detuning oi' the oscillation circuits is inevitable.

Hence, the condition of untuning would have to be corrected by the addition of condensers or coils. However, switches carrying radio frequency energy are undesirable because of additional damping and the requisite shielding.

Now, the invention discloses 'a circuit arrangement in which thesedrawbacks are avoided by reason that the switches carry no radio frequency energy or practically so. In one switch'position,

two paralleled series arrangements of condensers, all of like capacity, serve as a coupler capacity being common'to the oscillation circuits, whereas in the other switch position one of these condensers, to avoid detuning, is separately connected in each or the two oscillation circuits and another suitable coupling is chosen.

The invention shall be explained in more detail in what 1ollows and with reference to the accompanying drawing wherein:

, Fig. 1 shows the circuit organization of the invention, 1 Fig. 2 shows the circuit connections obtained when the switches are in the positions illustrated in Fig. 1 whereby transmission of a wide frequency band is effected, and Fig. 3 shows the circuit connections obtained when the switches are in the positions opposite to those illustrated in 4 Fig. l whereby-the transmission of a narrow frequency band is eflected.

Referring'to Fig. 1, there are shown a pair of coupled tuned circuits Cz-L. In one of ,the 1 switching positions, only the switch Si is closed so that the four similar condensers CI-Cl conjointly actlike a single condenser C1 of the size of the individual condensers as shown in Fig. 2. The coupling in this connection is'very close, for

which reason, to minimize crevasing or the production of a double peaked resonance curve,

damping resistances WI and W2 are included in the circuit. The coupling insured by condenser C, Fig. l, is only very loose contrasted with the coupling due to C1.

7 58 In the other switch position, switches s: mg

circuit in this condition is shown in Fig. 3. Condensers C3 and 04 as well as the resistances WI and W2 are thus rendered inoperative, while condensers Cl and 02 no longer operate as coupling condensers, but are merely included in the oscillation circuits and avoid detuning, for in the switch position shown in Fig. 3, each oscillation circuit CtL contains an additional condenser, namely, the coupling condenser Cl and C2, respectively. In the circuit illustrated in Fig. 3 the coupling between the oscillation circuits is effected only by condenser C and it is so loose that the ensuingband width is limited. But in lieu of this coupling also any other coupling could be employed.

What I claim is:

1. A band-pass filter network comprising a pair of similar, tunable circuits, each including an inductance, a variable condenser, a resistance and a. pair or fixed condensers all connected-in series in the order named, a series coupling condenser connected between high potential'ends of said inductances, a conductive connection between the low potential ends of said inductances, switch 25 mechanism. individually associated with each tunable circuit for short circuiting the resistance and one of the fixed-condensers when in closed position, and other switch mechanism conjointly associated with both tu'nabl'e circuits and connected between the respective junctions of the short circuited resistance andfixed condenser, whereby the frequency band to be transmitted may be selectively varied within wide limits without altering the tuning of the circuit, upon opening the first switch mechanism and closing the second switch mechanism, and vice versa.

. 2. A band-pass filter network comprising a pair of similar oscillation circuits, each comprising a variable condenser, an inductance, a resistance and two equal capacities, all connected in a closed circuit, a coupling condenser connected between the high potential ends of the two inductances, a conductive connection between the low potential ends of said inductances' 45 a switch connected between low potential ends of the two circuits, between the common terminals of the resistance and one of the two equal capacities in each circuit, and a switch in each circuit shunting said resistance and seldom of the two equal capacities, the arrangement being such that upon operation of the first switch to closed position and with the two last mentioned the closing of the two last mentioned switches and the opening of the first switch adjusts the circuits to pass a narrow band of frequencies. in each case the oscillation circuits being tuned to substantially the same resonant frequency.

3. A band-pass filter network comprising a pair of tunable circuits, each includingan inductance and a variable condenser, 15. series coupling condenser connected between the high potential ends 01 said inductances, a conductive connection between the low potential ends of said inductances, a plurality of fixed condensers common to said pair of tunable circuits and serving as a parallel coupling capacity, said series coupling condenser and'said parallel coupling to one capable of passing a narrow frequency band comprising a first switching mechanism for causing the plurality of fixed condensers to become ineflective as a parallel coupling capacity and a second switching mechanism individual to each tunable circuit for short circuiting certain 01 the fixed condensers and switching into said tunable circuits others of said fixed condensers.

- RUDOL'E WEBER. 

